You need to check the problems, that may be the following reasons:
Check if the AV cable is properly connected to the Xbox 360 and TV
make sure the cable is securely connected
Check the TV Settings
1. Make sure the TV's video playback system (PAL or NTSC) is set to the same as the Xbox 360 console.
2. If your Xbox 360 supports PAL, set your TV to PAL 60.
3. Turn off the correction feature of your TV such as Dynamic Comparison, Automatic correction, etc.
Reset your Xbox display settings
1. Remove the disc from the CD-ROM drive and restart the console.
2. After starting the console, press and hold the "Y" button on the controller and pull down the right trigger. The display settings will be reset to the default...